Photolithography is commonly used during formation of integrated circuits on semiconductor wafers. More specifically, a form of radiant energy (such as, for example, ultraviolet light) is passed through a radiation-patterning tool and onto a radiation-sensitive material (such as, for example, photoresist) associated with a semiconductor wafer. The radiation-patterning tool can be referred to as a photomask or a reticle. The term “photomask” traditionally is understood to refer to masks which define a pattern for an entirety of a wafer, and the term “reticle” is traditionally understood to refer to a patterning tool which defines a pattern for only a portion of a wafer. However, the terms “photomask” (or more generally “mask”) and “reticle” are frequently used interchangeably in modern parlance, so that either term can refer to a radiation-patterning tool that encompasses either a portion or an entirety of a wafer. For purposes of interpreting this disclosure and the claims that follow, the terms “reticle” and “photomask” are utilized interchangeably.
Advances in semiconductor integrated circuit performance have typically been accompanied by a simultaneous decrease in integrated circuit device dimensions and a decrease in the dimensions of conductor elements which connect those integrated circuit devices. The demand for ever smaller integrated circuit devices brings with it demands for ever-decreasing dimensions of structural elements, and ever-increasing requirements for precision and accuracy in radiation patterning.
Exemplary prior art processes for patterning radiation are described with reference to FIGS. 1-9.
Referring initially to FIG. 1, an exemplary reticle 10 is illustrated in a process for forming a radiation-intensity pattern in a radiation-imageable material 44 associated with an exemplary semiconductor construction 40.
The reticle includes a so-called main-field region 12, and a peripheral region 14 surrounding the main-field region. Dashed lines 15 are provided to diagrammatically illustrate boundaries between the peripheral region 14 and the main-field region 12.
Reticle 10 is shown comprising a base 16, a first layer 18 directly against the base, and a second layer 20 directly against the first layer. The base 16 can be a relatively transparent material, such as, for example, quartz; the first layer 18 can be a material of intermediate transparency, such as, for example, molybdenum silicide; and the second layer 20 can be a relatively opaque material, such as, for example, a material comprising, consisting essentially of, or consisting of chromium.
The terms “relatively transparent” and “relatively opaque” are utilized to indicate that the materials 16 and 20 are transparent and opaque, respectively, relative to one another. Material 16 will typically be substantially entirely transparent, and accordingly will typically have a transmittance of about 100%. Material 20 will typically be substantially entirely opaque, and accordingly will typically have a transmittance of about 0%. Material 18 will have a transparency intermediate the transparency of base 16 and layer 20, and can have a transmittance of, for example, about 6%. Accordingly, material 18 attenuates radiation, but is not entirely opaque to the radiation.
The main-field region 12 is shown having a plurality of patterned features 22, 24, 26 and 28 provided therein, and having a series of gaps 21, 23, 25, 27 and 29 between the features. Some of the features contain the relatively opaque material 20 (features 24 and 26) while others only contain the intermediate transparency material 18 (features 22 and 28). Features 24 and 26 will substantially block radiation, while features 22 and 28 will reduce an intensity of the radiation passing therethrough without entirely blocking the radiation. Features 22 and 28 can be used for changing more than just an intensity of the radiation. For example, features 22 and 28 can be used to impose a phase-shift on the radiation.
Exemplary radiation 30 is shown directed toward reticle 10 from above the reticle, and is shown passing through the main-field of the reticle. The radiation is patterned by the main-field of the reticle. Specifically, the radiation passing from the main-field of the reticle has a primary pattern of intensity imposed by the reticle.
The semiconductor construction 40 is shown beneath the reticle. The construction 40 comprises a substrate 42 having the radiation-imageable material 44 thereover.
Substrate 42 can comprise a monocrystalline silicon wafer at a processing stage of integrated circuit fabrication, and accordingly having various materials associated therewith. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Radiation-imageable material 44 can comprise, consist essentially of, or consist of photoresist.
Radiation patterned by the main-field 12 of the reticle forms a primary intensity pattern 46 within radiation-imageable material 44. The general location of the primary pattern is bounded by dashed lines 47, and features of the primary pattern are illustrated by dashed lines 49, 50 and 51.
The intensity of radiation within primary pattern 46 is diagrammatically illustrated by the depth of the radiation within material 44, with deeper regions indicating higher intensity and less deep regions indicating less intensity. The primary pattern has high-intensity regions 60, 62, 64, 66 and 68 corresponding to areas where radiation is passed through gaps 21, 23, 25, 27 and 29, respectively, of the main-field region 12 of the reticle. The primary pattern also has zero-intensity regions 70 and 72 where the radiation has been blocked by features 24 and 26, respectively, of the main-field region. Additionally, the primary pattern has intermediate intensity regions 74 and 76 where the radiation has been partially-blocked by the features 22 and 28, respectively, of the main-field region.
After the intensity pattern is formed within the radiation-imageable material 44, the material 44 can be subjected to development with an appropriate solvent to selectively remove either exposed or non-exposed regions of the material. The development will thus transfer a pattern into the material corresponding to either the shown pattern of intensity or an inverse of the shown pattern of intensity.
The process of FIG. 1 shows the reticle 10 utilized as a mask for patterning radiation. The reticle 10 is actually itself formed with patterned radiation, and accordingly can be considered to be formed with a prior masking step. The mask utilized for forming the reticle may be a physical mask similar to the reticle, or may be another structure which can pattern radiation intensity. For instance, reticles are frequently formed by electron-beam or laser beam imaging of radiation-sensitive materials associated with a reticle substrate. Electron beam or laser beam radiation is typically not patterned by passing the beam through a reticle, but rather is patterned by passing the beam through masking elements associated with a laser beam or electron-beam apparatus. The masking elements will form polygonal shapes from the beam, such as, for example, triangular shapes or rectangular shapes.
A general prior art process for creating and subsequently utilizing a reticle is described with reference to a flow chart in FIG. 2. A first step 100 of the FIG. 2 process comprises generating a first mask for reticle formation. This comprises identifying elements which are ultimately to be formed with the reticle, conducting optical proximity corrections and possibly other corrections which account for differences between the pattern formed in a reticle and the pattern obtained from the reticle (such corrections can, for example, account for interference effects which occur in light as openings in the reticle approach the wavelength of light), and calculation of a masking pattern to be utilized for forming the features in the reticle which can ultimately be utilized to pattern radiation during formation of desired features in a radiation-imageable material. As discussed above, the first mask may be a large mask like a reticle, but typically would be a radiation-modifying structure traveling with a laser beam or an electron beam during the writing of a desired pattern onto the reticle.
Step 102 of the FIG. 2 process has radiation provided through the first mask and onto a reticle substrate to form a desired pattern in the reticle substrate. Actually, the radiation would be utilized to form a pattern in a radiation-imageable material associated with the reticle substrate, and the pattern would then be transferred into the reticle substrate with a suitable etch. The formation of the pattern in a radiation-imageable material and subsequent transfer of the pattern to the reticle substrate can be a multi-step process comprising formation of a radiation-intensity pattern within the radiation-imageable material, development of the radiation-imageable material to convert the intensity pattern into a physical pattern within the radiation-imageable material, and utilization of the patterned radiation-imageable material during the etch of the underlying reticle substrate. After the etch to pattern the reticle substrate, the reticle substrate can be utilized as a mask for patterning a radiation-imageable material associated with a semiconductor substrate. Accordingly, the reticle substrate is considered to be a second mask, and the formation of the desired pattern in the reticle substrate is considered part of a process for generating the second mask from the reticle substrate.
In step 104 of the FIG. 2 process, radiation is provided through the second mask (i.e., the patterned mask formed from the reticle substrate) and onto a radiation-imageable material to form a desired pattern within the radiation-imageable material. The formation of the desired pattern within the radiation-imageable material can be considered to be part of a multi-step process. Specifically, the radiation patterned by the second mask can form an intensity pattern within the radiation-imageable material, and subsequently the material can be developed. Such development can selectively remove portions of the radiation-imageable material exposed to a threshold intensity of the radiation relative to other portions, or vice versa, depending on whether the radiation-imageable material is a positive resist or a negative resist. Regardless, the development transfers a pattern into the radiation-imageable material that is based upon the radiation pattern formed within the radiation-imageable material by the reticle.
Interference effects create several difficulties in attempting to form a desired pattern within a radiation-imageable material. Specifically, a pattern formed in a radiation-imageable material by radiation passing through a patterned mask will typically not be identical to the pattern present in the mask. The difference in the patterns is due to the openings in the mask being similar in size to the wavelength of radiation that is to be patterned by the mask. FIG. 3 illustrates an exemplary problem that can occur during fabrication of a radiation-patterning tool substrate. Specifically, FIG. 3 shows a substrate 110, and a desired pattern 112 that is to be formed in the substrate. The pattern 112 is a four-way intersection. The desired pattern is shown with dashed lines 114. Desired pattern 112 has square corners 116 (i.e., corners which are 90°) where segments join in the four-way intersection. Unfortunately, if the mask utilized to generate the image 112 is identical to the desired pattern of image 112, an image 118 having rounded corners 120 will result after the pattern is written into a radiation-imageable material and transferred into the substrate.
If the problematic reticle of FIG. 3 is subsequently utilized to transfer a pattern onto a radiation-imageable material associated with a semiconductor substrate, the problem of corner rounding can occur again so that the pattern transferred into the radiation-imageable material is even further removed from the ultimately-desired pattern. FIG. 4 illustrates an exemplary semiconductor substrate 122 comprising a radiation-imageable material 124 having a pattern 134 formed therein with the problematic reticle of FIG. 3. A desired pattern 126 is shown in dashed line in FIG. 4 for comparison to the pattern 134 that actually results. The desired pattern 126 is a four-way intersection having square corners 128. The actual pattern 134 has severely rounded corners 130, instead of the desired square corners 128.
A procedure which has been developed to address the problems of FIGS. 3 and 4 is described with reference to FIGS. 5 and 6. FIG. 5 is a diagrammatic representation of a mask 140 utilized to form segments of a reticle merging at relatively square corners. The mask comprises an open region 142, and blocked regions 144. The open region has segments 146, 148, 150 and 152 which merge at corners 154, 156, 158 and 160.
The mask is ultimately to be utilized for forming a four-way intersection of merging segments of a reticle, with the merging segments being patterned by the open region 142. Each of the corners 154, 156, 158 and 160 of mask 140 comprises a so-called anti-serif (with the anti-serifs being labeled as 162, 164, 166 and 168). The anti-serifs can compensate for the interference problems discussed above with reference to FIG. 3 so that the segments formed from the reticle join at substantially square corners, rather than at rounded corners.
As discussed previously, a reticle is typically formed by laser writing or e-beam writing so that the pattern of the reticle is directly written onto a radiation-sensitive material on the reticle substrate, with a shape of the energy beam being modified during the writing. The modification of the energy beam shape forms polygonal images during the writing, and can be considered to be masking occurring during the writing. Accordingly, the mask image of 140 may not exist as a single large mask, but rather can be accomplished with a dataset and a beam manipulation devise utilized during the writing of an image onto a reticle with an energy beam (such as, for example, an electron beam or laser beam).
The processing described with reference to FIG. 5 can form square corners on images patterned into a reticle. Similar processing can be utilized to form square corners on images formed in a radiation-imageable material utilizing the reticle. For instance, FIG. 6 shows a mask 170 corresponding to a reticle configured to form a four-way intersection in a radiation-imageable material. The reticle comprises a relatively transparent region 172, and relatively opaque regions 174. The relatively transparent region 172 comprises merging segments 176, 178, 180 and 182. The reticle further comprises anti-serifs 180, 186, 188 and 190 at corners where the segments merge. The anti-serifs can avoid the problem discussed above with reference to FIG. 4 so that a pattern created with the reticle will be a four-way intersection with square corners rather than the rounded corners discussed with reference to FIG. 4
Interference can create rounded corners on other structures besides intersecting segments. For instance, it is frequently desired to form segments having substantially square corners at ends of the segments. However, interference can lead to rounding of the corners. This problem is described with reference to a construction 200 of FIG. 7. The construction can be a radiation-patterning tool, or a semiconductor substrate. In either event, a mask is utilized to form desired images 202 and 204 on a radiation-imageable material 205 associated with an underlying substrate. (It is noted that the term “substrate” is broad enough as utilized herein that the radiation-imageable material can alternatively be considered part of the substrate.) The desired images are shown with dashed lines, and have ends 206 and 208 respectively, having square corners 203, 205, 207 and 209. Unfortunately, interference effects occurring during formation of the images leads to actual images 210 and 212 being formed which have rounded ends 211 and 213, respectively.
FIGS. 8 and 9 illustrate masking patterns which have been developed to avoid the problem discussed above with reference to FIG. 7. FIG. 8 shows a mask 220 having transparent regions 222 and 224, and having an opaque region 226. The transparent regions have serifs 228, 230, 232 and 234 associated therewith. The serifs are provided to avoid the rounding of the corners discussed above with reference to FIG. 7. FIG. 9 shows the mask 220 with hammerheads 236 and 238 utilized instead of the serifs.
The utilization of anti-serifs, hammerheads and serifs to avoid rounded corners creates several complications in the fabrication of masks. Accordingly, it is desired to develop alternative methods for alleviating, and preferably preventing, undesirable formation of rounded corners during patterning processes.